Anti-pollution apparatus

ABSTRACT

Apparatus for the generation of free radicals and admixture thereof with combustible pollutants for substantially complete elimination of such pollutants by oxidation or combustion.

United States Patent Gamble et al.

1451 Feb. 12, 1974 ANTI-POLLUTION APPARATUS Inventors: Slade B. Gamble, Park Ridge;

Richard A. Kelly, Prospect Heigh both of I11.

Assignee: Flinn & Dreffein Engineering Co.,

Northbrook, 111.

Filed: Nov. 24, 1971 Appl. No.: 201,885

u.s. c1 23 277 0, 423/210, 431/5,

431/174, 431/284 1m. (:1. 1323 9 114, Field of Search ..23/277 c; 423/210, 212;

References Cited UNITED STATES PATENTS 10/1966 Gary 23/277 C UX 10/1968 Burden, Jr. 23/277 C 9/1971 Nesbitt et al.... 1. 23/277 C 3/1972 .Reichhelm 23/277 C X Primary Examinerloseph Scovronek Attorney, Agent, or FirmMcD0ugall, Hersh & S00

ABSTRACT Apparatus for the generation of free radicals and admixture thereof with combustible pollutants for substantially complete elimination of such pollutants by oxidation or combustion.

8 Claims, 9 Drawing Figures 1 ANTI-POLLUTION APPARATUS This invention pertains to a novel and unique method and apparatus having improved efficiency for substantially complete oxidation of carbonaceous materials to molecular end products comprising essentially carbon dioxide (CO water vapor (H O) and nitrogen (N The method and apparatus is particularly adaptable to the oxidation of carbonaceous wastes which could otherwise become environmental pollutants.

Combustion has been employed for centuries to render carbonaceous or other combustible materials more innocuous to the environment of mankind; however, little more than greater emphasis upon the conditions of time, temperature and turbulence distinguishes contemporary methods and apparatus from the earliest use of fire for degradation of combustible pollutants.

Apparatus of prior disclosure stresses retention time (sometimes referred to as residence time) during which combustion reactions can be completed. A rule-ofthumb has placed a value upon retention time of about one second, with shorter time accruing to higher retention chamber temperatures and vice versa. However, there is a limit, or point of diminishing returns, for higher and higher temperatures. For one thing, temperatures in excess of about 2,800 F. are know to lead to production of another pollutant; namely, nitrogen oxides (NO These are now restricted to less than three parts per million (3 ppm) in ambient air by most of the environmental control codes. Also, higher temperatures in the retention chamber lead to dissociation or reversal of the normal exothermic combustion reactions unless ever increasing quantities of excess air are employed.

Apparatus of prior art is seriously limited and may even be rendered inoperative if directly exposed to pollutant combustibles containing more than 3 to 5 percent of combustion inhibitors, such as CO and H 0. The presence of such inhibitors in the zone of the apparatus containing the induction period of the reaction can produce extinguishment of the flame. This requirement for excluding combustion inhibitors from the induction zone wherein ignition commences sometimes precludes placement of apparatus of prior art in intimate and contiguous contact with the combustible pollutants.

It is an object of this invention to provide a method and apparatus which reduces retention time requirements for the combustion reaction without undesirable increase in retention chamber temperature and without utilization of excessive amounts of air whereby combustible pollutants such as carbonaceous materials, hydrogen, carbon monoxide andthe like can be removed to improve the environment without substitution of other pollutants.

Another object of this invention is to provide a method and apparatus which can be employed in intimate and contiguous contact with combustible pollutants to be processed therethrough without limitation by reason of the presence of combustion inhibitors, such as CO H and the like.

More specifically, it is an object of this invention to provide a method and means for efficient and substantially complete oxidation, as by combustion, of carbonaceous and other combustible materials, in which such oxidation is achieved at lower temperature and shorter time; in which utilization is made of a minimum amount of air; in which a minimum of other pollutants are formed as a consequence of removal of the original pollutants; in which the apparatus is simple in construction and easy in operation thereby to provide a relatively low cost unit which can be easily operated and controlled without the'need for highly skilled labor, and which is capable of low cost continuous operation for environmental control.

These and other objects and advantages of this invention will hereinafter appear and, for purposes of illustration, but not of limitation, embodiments of the invcntion are shownv in the accompanying drawings, in which FIG. 1 is a side elevational view of apparatus embodying features of this invention;

FIG. 2 is an elevational view in cross-section taken along the line 22 of FIG. 1, showing the free radical generator embodying features of this invention;

FIG. 3 is another embodiment showing a plurality of free radical generators;

FIG. 4 is a further embodiment of the invention, showing a modification of the generator system of FIG.

FIG. 5 is another embodiment for the introduction of combustible pollutants and auxiliary fuel in atomized liquid form; a

FIG. 6 is a diagrammatic view in cross-section of th arrangement of outlets from the various chambers;

FIG. 7 is a sectional view similar to that of FIG. 6 showing a further modification in the arrangement of outlets;

FIG. 8 is a sectional view similar to those of FIGS. 6 and 7 showing a still further modification in the construction and arrangement of the outlets; and

FIG. 9 is an elevational view showing the arrangement of the free radical generator in a commercial application of thisinvention.

An important concept of this invention resides in the method and apparatus for the efficient generation of free radical and the admixture thereof, before loss of life, with the pollutants for catalyzing the oxidation thereof, for more efficient and complete removal thereof, preferably though not necessarily in lesser time and at a lower temperature during passage of the pollutants with a carrier gas or fluid through the reaction chamber. The term free radicals refers to an atom or group of atoms having one or more unshared electrons which may enter into chemical bond formation and increases the activity of the atom while alive.

While it is believed that the new and novel effect can be explained by way of the efficient generation and utilization of free radicals of combustion, it will be understood that other theoretical considerations may be involved in the unique results which have been observed with the method and apparatus of this invention. Thus,

without restricting the invention to any particular theory, the following theoretical considerations are sub mitted for a better understanding of this invention.

Classical explanations of combustion reactions stress the influence of temperature upon the reaction rate. Some such explanations ascribe a doubling of the reaction rate for each 18 to 20 F increase in temperature. It will be obvious that this method of increasing the rate of reaction has limitations. Molecular dissociation takes place at increasing rates at higher temperatures, thereby to limit the temperature levels that may be employed and the increased production of nitrogen oxides at higher temperatures is also deleterious to clean thermal degradation.

Classical explanations of combustion reactions have not, however, commonly recognized the important role in combustion played by free radicals. There was scarce mention of these strong activators prior to the third decade of the twentieth century.

The unshared electrons of free radicals are capable of breaking the chemical bonds of the molecules comprising combustibles and oxygen upon collision with them at much lower kinetic energy that is required for breaking the molecular bonds by collisions between the molecules themselves in the absence of free radicals.

Unfortunately, free radicals have extremely short life, some existing for only afew microseconds and others for a few milliseconds. While free radicals can be extremely active in the role of breaking molecular chemical bonds and the subsequent forming of new chemical compounds, their short life makes them elusive for a deliberate employment in a combustion device.

Amongst the free radicals occurring in the combustion of carbonaceous material in air are: C CH, HCO, and OH. The identifiable free radicals are not at all limited by these, however, as the stripping of H from a hydrocarbon molecule will generate free radicals. The bydroxy (OH) radical is of prime importance and plays a role in the combustion of CO. It is well established that the addition of water to the combustible mixture of CO and hydrocarbons with air will increase the rate of development of thermal energy. There is evidence to the effect that the addition of water to such reactions increases the rate of heat development. It is thought that the OH free radical is the principal activator.

The present invention'pertains to apparatus which includes a free radical generator in association with a reaction zone in the form of a combustion chamber. Free radicals'are progressively created in such a fashion as to provide a plentiful supply of free radicals immediately" contiguous to the molecules of the combustible pollutants and oxygen containing air, with or without the addition of enriching fuel, for rapid and uniform admixture therewith.

Referring to the drawings for a more detailed understanding of the method and apparatus of this invention, there is shown in FIG. 1 an apparatus embodying the concepts of the invention, including a passage 12 for the transmission to the reaction zone, including a retention chamber 14 and a conduit section 18, of a gaseous carrier, including air, containing the pollutants adapted to be oxidized or otherwise consumed in accordance with the practice of this invention. Immediately in advance of the retention zone, the passage 12 is associated with a free radical generator 10. Waste material can be supplied to passage 12 in the form of a gas, vapor, a suspension of a liquid or solid in a gas, combustion air, etc. The free radical generator communicates with the retention chamber 14, which is preferably open at its opposite end 16 to the conduit section 18 preferably of frusto-conical cross-section. As can be seen in FIG. 1', the section 18 has diverging walls extending away from the free radical generator 10 toward retention chamber 14.

For a detailed description of the free radical generator, reference is made to FIG. 2 of the drawings. Circumscribing passage 12 is a small annular passage 22 defined by the wall l2 yof't he-passage and wall 24. The

generator 10 also includes a plenum chamber 26 which communicates with .the annular passage 22. Plenum chamber 26 is provided with inlet means 28 to supply a fuel or a mixture of fuel and combustion air thereto for passage through annular passage 22 to the outlet and adjacent to the discharge end 20 of passage or conduit means 12. In the preferred embodiment illustrated in FIG. 2, the annular passage 22 is concentric with the discharge end 20 of conduit means 12.

The free radical generator 10 also has an annular chamber 30 which is preferably concentric with both annular passage 22 and passage 12. In accordance with the practice of this invention, free radicals are generated by combustion of gaseous fuel and air in substantially stoichiometric proportion starting in chamber 30 and continuing outwardly into retention chamber frusto-conical section 18. I

The forward velocity of the gases issuing from the discharge opening 32 of chamber 30 unavoidably exert an inductive influence upon gases which are ambient to the opening 32. Aspiration of combustion inhibitors into the combustion induction zone, wherein combustion first begins, will produce extinguishment of the be ginning stages of combustion and every stage subsequent thereto. Such poisoning" of the induction zone of combustion devices is commonly the cause of flame extinguishment in high velocity burners.

This inductive influence is prevented from aspirating ambient gases which may contain combustion inhibitors, such as CO into the chamber and, particularly into the region of chamber 30 wherein the induction period of the combustion of the stoichiometric mixture is zoned. Discharge opening 32 of the chamber 30 presents a constricted area which causes chamber 30 to operate-at a pressure slightly greater than that of the ambient gases contained in the contiguous chamber 18. Said higher pressure is maintained at a sufficiently greater value than obtains in chamber 18 so that the inductive action of the forward velocity of the gases issuing from opening 32 cannot aspirate gases from chamber 18 into chamber 30. Likewise, aspiration of gases effluent from openings 20 and 22 into chamber30 is prevented by the higher pressure-maintained in chamber 30. In the preferred practice of this invention, the outlet 32 is constructed to direct theeffluent of flame and free radicals angularly in the direction toward the pollutant stream for effecting immediate admixture therewith and, importantly, to assist in blocking flow of gases containing combustion inhibitors from the reaction chamber 14-18 into the combustion chamber 30. In the illustrated modification, this is achieved by construction of the wall 31, away from the passage 12, as a converging wall on the outlet which slopes at an angle within the range of 2045 and preferably within the range of 2535.

The free radical generator of this invention includes means to supply an essentially stoichiometric mixture of fuel and air to chamber 30. As illustrated in FIG. 2, the generator has a plenum chamber 34 which is provided with inlet means 36 to supply stoichiometric mixture to chamber 34. A plurality of passages 38 distribute the stoichiometric mixture from plenum chamber 34 to chamber 30 wherein flame induction begins. 1f the areaof opening 32 from chamber 30 were not considered, the forward velocity of the 'fluid flowing through passages 38 would aspirate ambient fluids from chamber 14 and passage 18.back into chamber 30 in operation, the mixture of fuel and air in substantially stoichiometric proportion flows into chamber 30 wherein it is ignited as by means of an electric spark or other suitable ignition means. Means, not shown in the drawings, could be provided to communicate with chamber 30 for electronic supervision (ultra-violet detector or flame detection electrode) of the continuation of combustion in chamber 30. Such electronic supervisory devices are commonly known to those practiced in the arts of fuel combustion.

When ignition of the stoichiometric mixture in cham ber 30-is assured, a continuous, steady flow of free radicals from chamber 30 into chamber 18 ensues. Furthermore, the effluent gases from chamber 30 are very close to maximum flame temperature of the stoichiometric mixture. This may attain temperatures in the order of 3 ,000 F. The combination of this high temperature of the effluent from chamber 30 and the enrichment thereof with free radicals in abundant quantity provides for ignition and rapid combustion of combustible mixtures issuing from the annular openings 20 and 22 into chamber 18.

The gaseous fluids are issued from openings 20, 22 and 32 at turbulent velocities (having higher than critical Reynolds number) whereby thorough mixing is achieved in a period of time commensurateto the lifetime of the free radicals issued from the opening 32. Therefore, free radicals generated in chamber 30 and mixed with combustible mixture of gases effluent from openings 20 and 22 are available for their important role in combustion reactions.

In the case of turbulent flow of fluids in a duct at velocities above critical Reynolds Number, the random velocity of the fluid particles may be expressed as two components; namely, a forward component and a radial component which is normal to the forward component. The radial component is a measure of the mixing action of contiguous streams of fluids. It increases with the average forward velocity of the fluid particles approximately as the 0.83 power of the forward velocity:

Vr VIDA!!! Typically, the forward component of the velocity of the fluids effluent from openings 20, 22 and 32 is in the order of magnitude approximating or exceeding 200 feet per second. Therefore, the radial component of the random particle velocity approximately 80 feet per second. The distance between openings 32, 20 and 22 is less than one inch. The mixing time elapsing between generation of free radicals in chamber 30 and their encounter with molecules of fuel and oxygen is less than 0.001 second, well within the useful lifetime of the free.

radicals.

In accordance with the practice of this invention, a steady flow of free radicals is issued as effluent from the opening 32 of chamber 30. Duringthe induction phase of combustion, the free radicals must be shielded from combustion inhibitors until temperature of the burning gases is well above the minimum kindling temperature." The temperature of the gases effluent opening 32 is in the order of 3,000 F. At this temperature, or even half this temperature, combustion inhibitors may have some retarding effect upon flame velocity but the inhibitors are unable to stop the chain reactions of hydrocarbon combustion. Apparatus of the prior art does not afford the sheltering of the'induction zone from combustion inhibitors provided in the apparatus of this invention; particularly, by the over-pressure provided in chamber 30. Because of such shielding, it is possible to place the free radical generation chamber 30 in such close proximity to fluids which may contain quantities of CO and H 0 and therefore capable otherwise of producing almost instant flame extinguishmcnt in apparatus of prior art. Such close proximity of fluids and free radicals is essential to the efficient utilization of their activating effects upon breaking chemical bonds of molecules of fuel and air for cleanerand more rapid conversion of combustible pollutants to innocuous chemical compounds.

Other features of the present invention which provide higher efficiency, pollutant degradation at lower temperature and in shorter time, and with a minimum of excess air are outlined in the following paragraphs.

The oxygen carrying combustion air required for combustion of the pollutants is thoroughly premixed with the combustible pollutants before the mixture emerges into chamber 18 from opening 20..Th erefore, additional time is not required for such mixing before combustion of the pollutants is initiated by the hot, free radicals issuing from opening 32.

In event additional fuel is required and, when such enrichment with fuel is accomplished by a flow from opening 22, such fuel is premixed with sufficient air to promote a maximum rate of chemical cracking (a breaking up into simpler compounds by heating) of the additional fuel. Such cracking, which gives rise to additional free radicals, especially C CH, and HCO, having superior lifetimes, serves to further enrich the burning admixture of combustible pollutants and air with a fresh and augmented supply of free radicals in chambers 18 and 14.

The primary admixture of air with 'fuel supplied to the annular passage 22 is not critical. Some five to ID per cent of the stoichiometric proportion of air to fuel can be beneifical for enhancing the chemical cracking of the additional fuel.

Generally, the enthalpy supporting the free radical generator chamber 30 is negligible in comparison to the enthalpy of the combustible pollutants and that of additional enriching fuel. However, the enriching free radicals generated downstream of the opening 22 is, in many instances, very desirable for the fast, clean combustion of the combustible pollutants issuing from the opening 20.

Additional fuel introduced through outlet 22 as ring gas is desirable, in most instances, for combustion of and removal of combustible pollutants from the stream issuing from passage 12. Such ring gases, introduced between the effluent from the combustion chamber through outlet 32 and the pollutant stream, become immediately admixed with both streams which cause cracking of the hydrocarbon enrichment fuel for generation of additional free radicals upon combustion. Wlth such ring gas, the unit can be operated at lower temperature. This not only increases the efficiency of the unit, but it also enables operation with less nitrogen fixation or less oxides of nitrogen in the effluent from the unit.

Total combustion air admitted to chamber 14 should be in stoichiometric proportion i 5 percent. Combustion chambers of the types heretofore employed have required 50 to percent excess of combustion air'to assure complete degradation of combustible pollutants. One of the important advantages of this invention is the elimination of the need for unnecessary and uneconomical heating of excess air. I

Retention time required for completion of combustion of the pollutants, in accordance with the practice of the present invention, is sometimes as little as onefifth that required for apparatus of prior art.

Steady, uninhibited generation of free radicals originating in the induction zone of chamber 30 and continuingin chamber 18 and their substantially instantaneous and uniform admixture with the pollutants, in accordance with the practice of this invention, keep the combustion process of the pollutants supplied with these activators in a manner that can utilize the free radicals within their short-lived existence. Maximizing the generation of free radicals and their utilization in the thermal degradation process as well as the apparatus for effecting the same in an efficient and economical manner represents one of the important concepts of this invention. 7

A prototype model of the present invention has been constructed and operated with thefollowing results, the description of which is given by way of illustration, but not by way of limitation, it being understood that changes in size, dimension, capacity, and fuel may be made. I

Dense-black carbonaceous smoke (Ringelmann No. was generated by partially burning old rubber automobile tires in a chamber discharging into conduit means 12. The smoke was inducted into the conduit means by an airjet discharging thereinto in accordance with the well known principle of a jet pump. The jet of air supplied complete combustion air requirements for the combustible pollutants and for auxiliary natural gas fuel supplied with a small amount of air through annular opening 22 ofthe free radical generator. The volume of air supplied through the induction jet was ade quate to supply the stoichiometric requirements of approximately 6,000,000 to 7,500,000 Btu per hour of typical hydrocarbon fuel which can be calculated at 100 to 125 Btu per standard cubic foot of air at 60 F and 29.92 inch Hg absolute pressure, without appreciable error.

The plenum 34 of the free radical generator was supplied with about 1 14,000 Btu per hour of stoichiometric natural gas and air mixture at 10 inches of water column pressure. The annulus 22 of the free radical generator was supplied with 2,000,000 to 2,500,000 Btu per hour of natural gas with less than 10 percent aeration to stoichiometric proportions.

At black temperatures in retention chamber 14 (less than l,200 F), the dense black smoke was admitted to chamber 14 with only the small amount of gas burning in chamber 30 and short blue flame issuing from opening 32. The black smoke proceeded through chamber 14 and issued in a completely opaque plume from the discharge end 16.

Combustion of the pollutant smoke and fume was completed under essentially stoichiometrically proportioned air and fuel without odor or any visible effluent from chamber 14. 4

The length of chamber 14 was seven feet and its diameter was one foot ten inches. Chamber 18 was one foot long. At 2,400 F, the retention time in chamber 14 was calculated to be slightly under 0.2 second.

The dense black smoke resulting from the partial combustion of automobile tires was repeatedly exposed to the degradation of the free radical generator with immediate results described above. If the free radical generator was turned off, the smoke poured from the discharge end of chamber 14 in black profusion. Reactivation of the free radical generator immediately consumed the smoke and all other combustible pollutants so that the effluent from the apparatus was again clean and free of smoke. l

The shortness of the retention time and thesmall amount of auxiliary fuel (less than a third of the total enthalpy of the process) and the completeness of the combustive degradation are of considerable importance to the commerical acceptance of an antipollution device of the type described.

In event that the capacity requirements are so large that the admixture of the free radicals with combustible pollutants within the lifetime of the free radicals cannot reasonably be accomplished; that is, in expanded size of the apparatus, a multiplicity of smaller sized free radical generators can be used. Such multiple use of the free radical generators could take such form as illustrated in FIGS. 3 and 4.

Of course, a multiplicity of entirely independentfree radical generators with independent retention chambers as illustrated in FIG. 1 could also be utilized to increase the capacity of combustible pollution abatement facilities.

The foregoing description and drawings of the method and apparatus of this invention should not be construed to in any manner limit the means which may be employed to achieve an admixture of combustion air and combustible pollutants to the jet pump described. Any other means which are well known to those versed in the arts of combustion may be employed. Such means might include mechanical mixing as in a fan or blower, nozzle mixing of converging streams of fluids, tortional shearing induced by directing vanes in the ducts carrying the fluids. Means for dispersion of liquid fluids in gaseous fluids and means for dispersion of solids having small particle size in gaseous fluids in the practice of this invention should likewise not be limited by any part of these specifications.

For example, as illustrated in FIG. 5, the pollutants, in the form of carbonaceous particles, can be atomized as they issue from the nozzle 50 in feed line 52 for dispersion as fine particles 54 in the converging stream of high pressure air for passage into conduit l2.

Returning now to a more theoretical description of the operation, the free radicals are directed by the wall 31 or by angling the outlet 32 in the direction towards the outlet for the stream of combustible pollutants issuing from passage 12 into chamber 14-18. This acceler- -ates admixture in a time period less than the life of the free radicals, such as within 1-5 milliseconds. This then defines the limitation with respect to the spaced relation between the outlet 32 from the generator 10 and the edge of the stream issuing from the passage 12 as well as the cross section thereof.

lt is for this reason that, in the preferred construction, the outlets are arranged as annular sections, as illustrated in FIGS. 6, 7 and 8. In FIG. 6, the passage 12 is in the form of an annulus, surrounded by an annular outlet 22 for the ring gas, which in turn is surrounded by an annular outlet 32 for the free radical containing flame stream. This keeps the stream 12 sufficiently close to the outlet 32 for admixture with all of the pollutant containing stream within the few milliseconds life of the generated free radicals. Thus the dimensions and the spaced relations between streams l2 and 32 can properly be defined by reference to the life time of the free radicals and preferably with a spaced relation and dimension which is less than the life span of the free radicals, with the gases flowing above the critical Reynolds number.

Even more intimate and immediate admixture can be effected by the arrangement shown in FIG. 7 in which the pollutant stream 12 is concentrically arranged between adjacent inner and outer outlets 22 for ring gas, which, in turn, are concentric with inner and outer outlets 32 from free radical generators.

It will be apparent that the concentric arrangement described can be continued to provide units of larger capacity without increase in area of stream 12 to the area and distance from generator 32 whereby some of the pollutants will not be admixed with free radicals for combustion and will remain as pollutants in the exhaust from the unit.

In the described modifications, the angular directing wall of the combustion chamber should be angled in the direction to project the effluent from outlet 32 into the pollutant stream.

While the invention has been described with reference to annular passages and outlets, it will be understood that such passages may be of other configurations, such as oblong, square, polygonal shape or the like, as illustrated in FIG. 8.

As illustrated in the composite drawing of FIG. 9,. the free radical generator extends rearwardly of the reaction chamber and sufficiently separated therefrom to permit cooling as by means of a jacket through which a coolant, such as air, water or the like, can be circulated to increase the working life of the unit to minimize replacement or repair. The accessibility to the free radical generator also enables replacement or repair to be effected in a simple and easy manner.

lt will be understood that changes may be made in the details ofconstruction, arrangement and operation, without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. A device for removal of combustible pollutants in an air stream comprising a main passage, means for flowing a continuous stream of a gaseous carrier through said main passage with the pollutants suspended therein in finely divided form, a free radical generator separate and apart from the main passage but adjacent thereto including a mixing chamber, a combustion chamber having an inlet portion communicating with the mixing chamber and'an outlet alongside the stream containing the pollutant issuing from the main passage, means for feedng a gaseous hydrocarbon and ox'ygen'containing gas in substantially stoichiometric proportion for complete combustion to the mixing chamber for flow from the mixing chamber to the combustion chamber wherein the mixed gases are ignited, means for igniting the mixture in the combustion chamber in advance of the outlet, and means for maintaining the gaseous mixture in the combustion chamber under pressure sufficient for issuance of the effluent at a velocity which exceeds the critical Reynolds number for turbulent flow for admixture with the pollutants immediately upon issuance from the combustion chamber, whereby free radicals generated during the combustion are immediately admixed with the pollutants to catalyze combustion and in which the outlet from the combustion chamber immediately surrounds the stream which issues from the main passage.

2. A device as claimed in claim I which includes an oxidation chamber contiguous with the outlet end of the main passage and into which the burning mixture from the combustion chamber and the gaseous stream from the mainpassage effluent for admixture and in which the portion of the oxidation chamber immediately following the main passage is tapered outwardly for gradual increase in cross-section.

3. A device as claimed in claim 1 which includes more than one free radical generator distributed through the cross section of the main passage at the outlet end thereof.

4. A device as claimed in claim 1 which includes an auxiliary passage between the main passage and the combustion chamber, having an outlet coincident with the outlet from the combustion chamber, means for feeding a mixture of oxygen containing gas and gaseous hydrocarbon to the auxiliary passagefor admixture with the effluent from the combustion chamber and main passage as additional fuel for combustion.

5. A device as claimed in claim 1 in which the main passage is in the form of an annulus and the outlet from the combustion chamber is also in the form of an annulus which is concentric with and immediately surrounds the main passage at the outlet from the combustion chamber.

6. A device as claimed in claim 1 in which the main' passage is in the form of an annulus and which includes a pair of combustion chambers having separate outlets with the outlet from one chamber comprising an annulus concentric with the main passage and immediately surrounding the main passage at the outlet from the combustion chamber and the outlet from the other chamber comprising an annulus concentric with the main passage and located immediately inwardly of the main passage at the outlet from the combustion chamber.

7. A device as claimed in claim 4 in which the main passage is in the form of an annulus and in which the outlets of the auxiliary passage and the combustion chamber are in the form of annuli concentrically arranged about the main passage.

8. A device as claimed in claim 4 in which the main passage is in the form of an annulus and the outlets from the auxiliary passage and the combustion chamber are in the form of annuli which are concentric with the main passage with one pair located outwardly of the main passage and another pair located inwardly of the main passage.

l Patent No. 3, 791, 796

Inven'tor(s) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated February 12, 1974 Slade B. Gamble; Richard A. Kelly It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

column 4, line 65, change "considered" to "constricted" Signed andsealed this 30th day of July 197 Attesting Officer (SEAL) At-test:

MCCOY M. GIBSON JR. 0. MARSHALL DANN Commissioner of Patents 

2. A device as claimed in claim 1 which includes an oxidation chamber contiguous with the outlet end of the main passage and into which the burning mixture from the combustion chamber and the gaseous stream from the main passage effluent for admixture and in which the portion of the oxidation chamber immediately following the main passage is tapered outwardly for gradual increase in cross-section.
 3. A device as claimed in claim 1 which includes more than one free radical generator distributed through the cross section of the main passage at the outlet end thereof.
 4. A device as claimed in claim 1 which includes an auxiliary passage between the main passage and the combustion chamber, having an outlet coincident with the outlet from the combustion chamber, means for feeding a mixture of oxygen containing gas and gaseous hydrocarbon to the auxiliary passage for admixture with the effluent from the combustion chamber and main passage as additional fuel for combustion.
 5. A device as claimed in claim 1 in which the main passage is in the form of an annulus and the outlet from the combustion chamber is also in the form of an annulus which is concentric with and immediately surrounds the main passage at the outlet from the combustion chamber.
 6. A device as claimed in claim 1 in which the main passage is in the form of an annulus and which includes a pair of combustion chambers having separate outlets with the outlet from one chamber comprising an annulus concentric with the main passage and immediately surrounding the main passage at the outlet from the combustion chamber and the outlet from the other chamber comprising an annulus concentric with the main passage and located immediately inwardly of the main passage at the outlet from the combustion chamber.
 7. A device as claimed in claim 4 in which the main passage is in the form of an annulus and in which the outlets of the auxiliary passage and the combustion chamber are in the form of annuli concentrically arranged about the main passage.
 8. A device as claimed in claim 4 in which the main passage is in the form of an annulus and the outlets from the auxiliary passage and the combustion chamber are in the form of annuli which are concentric with the main passage with one pair located outwardly of the main passage and another pair located inwardly of the main passage. 